Re: Reducing memory requirements for high extent xfs files

[Vlad Apostolov <vapo@sgi.com>]

Vlad Apostolov wrote:
> Michael Nishimoto wrote:
>>
>>
>> David Chinner wrote:
>>> On Wed, May 30, 2007 at 09:49:38AM -0700, Michael Nishimoto wrote:
>>>  > Hello,
>>>  >
>>>  > Has anyone done any work or had thoughts on changes required
>>>  > to reduce the total memory footprint of high extent xfs files?
>>>
>>> We changed the way we do memory allocation to avoid needing
>>> large contiguous chunks of memory a bit over a year ago;
>>> that solved the main OOM problem we were getting reported
>>> with highly fragmented files.
>>>
>>>  > Obviously, it is important to reduce fragmentation as files
>>>  > are generated and to regularly defrag files, but both of these
>>>  > alternatives are not complete solutions.
>>>  >
>>>  > To reduce memory consumption, xfs could bring in extents
>>>  > from disk as needed (or just before needed) and could free
>>>  > up mappings when certain extent ranges have not been recently
>>>  > accessed.  A solution should become more aggressive about
>>>  > reclaiming extent mapping memory as free memory becomes limited.
>>>
>>> Yes, it could, but that's a pretty major overhaul of the extent
>>> interface which currently assumes everywhere that the entire
>>> extent tree is in core.
>>>
>>> Can you describe the problem you are seeing that leads you to
>>> ask this question? What's the problem you need to solve?
>>>
>>> Cheers,
>>>
>>> Dave.
>>> -- 
>>> Dave Chinner
>>> Principal Engineer
>>> SGI Australian Software Group
>>
>> I realize that this work won't be trivial which is why I asked if anyone
>> has thought about all relevant issues.
>>
>> When using NFS over XFS, slowly growing files (can be ascii log files)
>> tend to fragment quite a bit.  One system had several hundred files
>> which required more than one page to store the extents.  Quite a few
>> files had extent counts greater than 10k, and one file had 120k extents.
>> Besides the memory consumption, latency to return the first byte of the
>> file can get noticeable.
>>
>>   Michael
>>
> Hi Michael,
>
> You could use XFS_XFLAG_EXTSIZE and XFS_XFLAG_RTINHERIT flags to
> set extent hint size, which would reduce the file fragmentation in 
> this scenario.
> Please check xfcntl man page for more details.
>
> Regards,
> Vlad
I meant XFS_XFLAG_EXTSZINHERIT not XFS_XFLAG_RTINHERIT. This one
should be set on a parent directory.

Regards,
Vlad